Here's why:

* Eukaryotic cells have a true nucleus that contains their DNA, as well as other membrane-bound organelles.

* Prokaryotic cells lack a nucleus and other membrane-bound organelles. Their DNA is located in a region called the nucleoid.

Protists are a diverse group of single-celled or simple multicellular organisms that are neither animals, plants, nor fungi. They are classified as eukaryotes because they have cells with nuclei and other membrane-bound organelles.